In the agricultural industry, plant disease control agents, namely agricultural chemicals, are used for the purpose of controlling plant diseases in the manner of fungicides and the like with the objective of reducing labor and stabilizing the quality and yield of agricultural products, and are essential for present-day agriculture in terms of ensuring safe and reliable agricultural products. However, as a result of having frequently or excessively used numerous chemical agents having the same mechanism of action among plant disease control agents to a specific plant disease as a target for control, a phenomenon is occurring in which target plant disease pathogens develop tolerance to agricultural chemicals having that mechanism of action.
On the other hand, there has recently been a growing interest among consumers in agricultural products grown with reduced levels of agricultural chemicals as well as social interest in reducing the environmental effects of chemically synthesized plant disease control agents. Amidst these circumstances, there is a desire for plant disease control agents and plant disease control methods that have less effect on the environment in comparison with conventional chemically synthesized plant disease control agents, have a broad spectrum against various plant diseases, and are effective even against resistant microorganisms for which existing plant disease control agents are no longer effective.
Monosaccharides are sugars that are the constituent elements of polysaccharides or oligosaccharides that cannot be further hydrolyzed, and are typically classified into aldoses, ketoses, sugar alcohols (polyols) and the like according to functional groups contained in their chemical structures. Examples of aldoses include glucose, mannose, allose, altrose, talose, galactose, idose, gulose, ribose, lyxose, xylose, arabinose, erythrose, treose and glyceraldehyde; examples of ketoses include fructose, psicose, tagatose, sorbose, xylulose, ribulose, erythrulose and dihydroxyacetone; examples of sugar alcohols include glucitol, mannitol, altritol, iditol, allitol, galactitol, arabitol, xylitol, ribitol, threitol, erythritol, glycerin, inositol and quercitol. In addition, nearly all of these have D-form and L-form optical isomers.
Some monosaccharides are known to enhance disease resistance in plants when administered to a plant (Patent Documents 1 and 2). In addition, monosaccharides have been reported to be effective as plant disease control agents with respect to actual plants. For example, D-tagatose has been determined to exhibit control effects against diseases caused by obligate parasites, such as microorganisms causing downy mildew (such as Pseudoperonospora cubensis, Plasmopara viticola or Peronospora parasitica), microorganisms causing powdery mildew (such as Sphaerotheca fuliginea) or microorganisms causing rust disease (such as Puccinia recondita), and diseases caused by oomycetes such as Phytophthora infestans or Pythium species, and to be useful as plant disease control agents (Patent Document 3). In addition, D-talose has been determined to be effective as a control agent of plant diseases caused by Magnaporthe grisea, Colletotrichum orbiculare, Alternaria brassicicola, Cochliobolus miyabeanus, Venturia inaequalis, Blumeria graminis f. sp. hordei, Sphaerotheca fuliginea, Xanthomonas oryzae pv. oryzae, Pseudomonas syringae pv. lachrymans and Ralstonia solanacearum, L-fructose has been determined to be effective as a control agent of plant diseases caused by Colletotrichum orbiculare, Alternaria brassicicola, Pythium species causing of damping-off of cucumber seedlings, Pseudomonas syringae pv. lachrymans and Ralstonia solanacearum, D-allose has been determined to be effective as a control agent of plant diseases caused by Magnaporthe grisea, Colletotrichum orbiculare, Alternaria brassicicola, Sphaerotheca fuliginea, Phytophthora infestans, Pseudoperonospora cubensis and Pythium species causing damping-off of cucumber seedlings, D-psicose has been determined to be effective as a control agent of plant diseases caused by Magnaporthe grisea, Colletotrichum orbiculare, Blumeria graminis f. sp. hordei, Sphaerotheca fuliginea, Pseudomonas syringae pv. lachrymans and Ralstonia solanacearum, D-galactose has been determined to be effective as a control agent of plant diseases caused by Rhizoctonia solani, Pythium species causing damping-off of cucumber seedlings, Phytophthora infestans and Erwinia carotovora subsp. carotovora, D-sorbose has been determined to be effective as a control agent of plant diseases caused by Pseudomonas syringae pv. lachrymans and Ralstonia solanacearum, D-mannose has been determined to be effective as a control agent of plant diseases caused by Pseudomonas syringae pv. lachrymans, and D-mannitol has been determined to be effective as a control agent of plant diseases caused by Xanthomonas oryzae pv. oryzae and Pseudomonas syringae pv. lachrymans (Patent Documents 4 and 5). However, the comparatively high treatment concentrations of these monosaccharides as plant disease control agents, and their inadequate dilutability and dispersibility when dissolving the monosaccharides in a spray solution to prepare chemical agents, have been indicated as problems.
Combinations of D-tagatose with other sugars and substances having bactericidal and/or fungicidal action are described in Patent Document 3 with respect to synergistic control effects resulting from combining monosaccharides with other substances. However, test examples are indicated only for neutral monosaccharides as the other monosaccharides, while there is no description of the efficacy of disaccharides or other sugars.
In addition, surfactants have widely been known to be able to be used to enhance the efficacy of chemical agents used as agricultural chemicals. However, since agricultural chemicals are usually liposoluble compounds and the prior art has attempted to enhance the efficacy of such compounds, which is for a stronger sense of compound-stabilizing efficacy rather than enhancing efficacy.
On the other hand, monosaccharides are compounds that exhibit extremely high water solubility and are present in an equilibrium state of α-pyranose, β-pyranose, α-furanose, β-furanose and linear structures in an aqueous solution, therefore the effects of conventional agricultural chemical assistants on such compounds was completely unknown. Although monosaccharides have been described in Patent Documents 3, 4 and 5 as being effective as plant disease control agents, and it is also described that various surfactants can be used as assistants for enhancing efficacy, there are no test examples regarding the efficacy of actual assistants.